1. Field of the Invention
The present invention relates to a solar thermal power generation system.
2. Description of the Related Art
As an example of a solar thermal power generation plant capable of efficiently accumulating solar heat, there exists a solar thermal power generation plant comprising a solar heat collection device which generates superheated steam by using water/steam (water vapor) as the primary heat medium, a solar heat accumulation/radiation device which uses molten salt or oil as the solar heat accumulation/radiation heat medium, and steam turbine power generation equipment which uses steam (water vapor) as the secondary heat medium (see JP-2014-92086-A, for example).
There also exists a solar thermal power generation plant comprising a high-temperature molten salt tank which stores high-temperature molten salt supplied from a heat collector by using molten salt as the primary heat medium and the heat accumulation/radiation heat medium while using steam (water vapor) as the secondary heat medium and a low-temperature molten salt tank which stores the molten salt after being used for heating the secondary heat medium driving the steam turbine (see “Crescent Dunes” [online]. Solar Reserve, LLC. [retrieved 20, May 2015]. Retrieved from the Internet: <URL: http://www.solarreserve.com/en/global-projects/csp/crescent-dunes> (hereinafter referred to as a “Non-patent literature 1”), for example).
As shown in FIG. 7 (conceptual diagram showing the configuration of a conventional solar thermal power generation plant), this solar thermal power generation plant comprises heliostats 200 as sun tracking mirrors configured to change their positions depending on the direction of the sun in order to efficiently collect the heat of direct sunlight (heat radiation from the sun) in the heat collector, a primary system A as a solar heat collection/accumulation system in which molten salt is circulated as the primary heat medium, and a secondary system B which carries out the electric power generation by driving the steam turbine with the steam (water vapor) as the secondary heat medium.
The primary system A includes a low-temperature molten salt tank 201, a first molten salt pump 202, a heat collector 203, a high-temperature molten salt tank 204, a second molten salt pump 205, a superheater 206, a reheater 207, an evaporator 208, and a feed-water preheater 209. The low-temperature molten salt tank 201 stores the low-temperature molten salt. The first molten salt pump 202 draws out the low-temperature molten salt from the low-temperature molten salt tank 201 and sends out the low-temperature molten salt. The heat collector 203 collects the heat of direct sunlight from the heliostats 200 and thereby heats up the molten salt sent out from the first molten salt pump 202. The high-temperature molten salt tank 204 stores the high-temperature molten salt heated by the heat collector 203. The second molten salt pump 205 draws out the high-temperature molten salt from the high-temperature molten salt tank 204 and sends out the high-temperature molten salt. The superheater 206, reheater 207, evaporator 208 and feed-water preheater 209 are supplied with the high-temperature molten salt from the second molten salt pump 205 and thereby heat up feed-water and the steam (water vapor) as the secondary heat medium. The molten salt after being cooled down due to the heating of the feed-water in the feed-water preheater 209 is stored in the low-temperature molten salt tank 201.
The secondary system B includes a high-pressure turbine 301, an intermediate/low-pressure turbine 302, an air-cooled steam condenser 303, a condensation tank 304, a feed-water pump 305, and a generator 306. The high-pressure turbine 301 is driven by superheated steam supplied from the superheater 206. The intermediate/low-pressure turbine 302 is driven by reheated steam supplied from the reheater 207. The air-cooled steam condenser 303 condenses the secondary heat medium after finishing the work in the intermediate/low-pressure turbine 302. The condensation tank 304 stores the condensed water. The feed-water pump 305 sends out the feed-water from the condensation tank 304 to the feed-water preheater 209. The generator 306 is driven by the high-pressure turbine 301 and the intermediate/low-pressure turbine 302 and carries out the electric power generation.
In this solar thermal power generation plant, during the nighttime, it is possible to heat up the secondary heat medium by supplying the high-temperature molten salt stored in the high-temperature molten salt tank 204 to the superheater 206, the reheater 207, the evaporator 208 and the feed-water preheater 209 and recovering the molten salt into the low-temperature molten salt tank 201, without supplying the molten salt from the low-temperature molten salt tank 201 to the heat collector 203 and the high-temperature molten salt tank 204. Therefore, the power generation can be carried out during the nighttime by driving the high-pressure turbine 301 and the intermediate/low-pressure turbine 302 with steam generated by heating up the secondary heat medium.